Twitter OAuth is broken
Trying to use the "Connect Twitter" button moves the user on to https://bridge.joinmastodon.org/users/auth/twitter but causes a HTTP 500 (e.g. x-request-id 650cdc54-1777-4b1d-961d-0cd4a49fcfb7).
This has been reproduced by myself and one of my mutuals. I've verified that I do not have an active Twitter app authorisation for the Bridge app.
We're both using Firefox 64 on Linux (Solus 3.999 and Ubuntu 18.04.1 respectively).